Inductance coil of the sliding core type



June 16, 1953 H. M. vlscH 2,642,559

INDUCTANCE COIL OF THE SLIDING CORE TYPE Filed Dec. 8. 1949 I :s J5 f5 5 INVENTOR.

HENRI MARINUS VISCH AGENT Patented June 16, 1953 INDUCTANCE COIL F THE SLIDING `CORE TYPE Henri Marinus Visch, Eindhoven, Netherlands, assigner to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 8, 1949, Serial No. 131,719 In the Netherlands December 11, 1948 7 Claims. (Cl. 336-30) This invention relates to inductance coils of the sliding-core type.

If, for example in radio receivers, use is made of two or more sliding-core inductance coils actua-ted by the same driving member, particular correction means are required to ensure a corresponding variation of the inductances of the two coils as a function of the position of the tuning member (tuning curve). Even when using one coil only it may be desirable to alter the tuning curve in accordance with that of a different element or component, for example to accord with the indication given by a tuning dial.

It is usually endeavoured to act upon the tuning curve separately at the two ends and centrally. For this purpose several means are known.

In French patent specification No. 895,839 is described an inductancev coil of the sliding-core type comprising a ferromagnetic correction body, arranged near the rear end of the sliding core (i. e. the end that enters the coil last) and which follows the movement of this core, the correction body being shaped in the form of a discI or cup and being adapted to be screwed over a bolt secured at the end of the core in line therewith. The spacing between the correction body and the end of the core acts upon the tuning curve primarily at the end which corresponds to the maximum inductance.

The present invention relates to an inductance coil of the sliding-core type comprising a ferromagnetic correction body arranged in a similar manner and has for its object to provide a simple and cheap construction.

According to the invention, an inductance coil of the sliding-core type comprising a ferromagnetic correction body which is arranged near the rear end of the sliding core and which follows I the movement of this core, is characterized in that the correction body is constituted by at least one rod or strip of sintered, ceramic, ferromagnetic material having a permeability of at least 100, the correction body and the core being secured to a common non-magnetic support so that the correction body is slidable substantially parallel to and axially of the core. Said ferromagnetic material may be of the kind which is primarily constituted by a magnetic ferrite and will be referred to hereinafter as ferrite.

Ihe high permeability `of the ferrite ensures a suflicient margin of correction even when using a small, and thus cheap, rod-shaped correction body. Without the use of a screw-thread such a rod may be arranged in a very simple manner so as to be slidable with some friction in the non-magnetic support. The part of the rod which projects beyond the coil winding after correction and with the core entirely within the coil winding does not substantially aiect the tuning curve and may be severed, so as to minimize the length of the coil construction.

In order that the invention may be more clearly understood and readily carried into eiTect, it will no-w be described more fully with reference to the accompanying diagrammatic drawing, given by way of example, in which Figs. 1 and 2 are front and side viewsof an embodiment of the invention comprising two coils;

Fig. 3 is a sectional View taken on` the vertical axis of one of the coils, and

Fig. 4 is a cross-sectional view taken on the line IV-IV of Fig. 3 and which shows one of the coils in greater detail.

Referring now to the drawing, Figs. 1 and 2 show the arrangement'of the two coils. Each coil is enclosed in a metal screening can I and 3, respectively, which cans are secured to a U- shaped frame I made of sheet material. The drive is eiected with the use. of a common shaft 9 on which are seated `two gear wheels I I and I3.

Fig. 3 is a sectional view of the rear coil of Fig. 1. The hollow sliding core I5, which is preferably made of ferrite, is secured to a. transverse partition I'I of a substantially tubular insulating support I1 made of plastic material and adapted to slide in and be guided by the screening can 3. The core I5 is driven by a gear wheel II which, through an aperture in the can 3, engages a toothed rack I3 pro-vided externally of the support II. In the position sho-wn, the core I5 is within a coil winding 2l almost to the maximum possible extent. The coil winding 2l surrounds an insulating cylinder 23.. The latter forms a unit preferably of plastic material coinprising an insulating base 25, which is secured in the screening can 3 with the use of a bolt 2l which also secures an insulating plate 29 and one end of a spring 3l which can be in the form of a bent `fiat steel strip as shown. The other end of the spring 3I is secured to the bottom of the U-shaped frame l. The resilience of the strip 3| holds the toothed rack I9 of the support I1 in engagement with the gear wheel I I. A rigid wire strap 36 prevents the toothed rack disengaging from the gear wheel.

The coil system is mounted on a chassis plate 33 with the use of several bolts. Several soldering tags 34 are secured to the base 25 by flanging, which tags 34 extend outwardly through apertures provided in the front surface of the can 3. The chassis plate 33 is provided with similar apertures to allow the soldering tags to pass.

At and adjacent the position of maximum insertion of the core into the coil Winding, the inductance of the coil maybe re-adiusted with the use of a smooth rod or stud 35 of' ferrite. The material of the stud may be of the kind described in British patent specification No. 626,946 with a' permeability of approximately 400.

The stud 35 is taken through an aperturein. the transverse partition I1 and is adapted to move therein with a certain amountlof friction;

the stud being urged by a smallY springv 31 into a"- slot provided on the inner surface of `thetubular initial positions-otherfthanthat of maximum in sertion of thecore I;` the stud; is substantially completely outside the coil field. Even in theposition inV which about half the core is inserted in the coil 2|, the effect of the studV 35 is still small. Subsequent to re-adjustment, the stud is secured with the use of lacquer and the part extending beyond the support' I "I, that is to say', the part' extending beyond the coil winding', with complete insertion` (shown in brok'enlines in Fig. 3) is cut off.

It will be notedthat'in the coil thus finally adjusted the stud 35 is no longer slidable relatively to the support II and the term slidable is to be understood to lmean that the stud is initially slidable, even though subsequent measures are taken to secure thel stud in position.

Instead of having. a smooth surface, the studr and constitute amagnetic screening between'zthe coil winding 2| and the screening' can 3; Owingi to the high'permeability' of the rods, the'greaterfy part ofthe lines of force of the coil complete` their circuit through these rods. Theremaining part strikes theA screening can` 3 and resultsv in eddy current losses therein. However, owing to the presence of the rods 43, this partisismall; so that the said losses are not troublesome.`

Similar rods may be arranged on the side: of the coil 2| adjacent the stud. 35. It should, how'-l ever, vbe considered that these rods attenuate the effect of the stud 35 on theV inductance of the' coil, so that the effect of this stud isreduced.

One ofthe ends'of theshaft 9 is journalled'in an insulating bearingV 4I (Fig. 2)' so as to pre"-v vent the frame l from forming, together with the` shaft 9, a closed circuit, which would result in. undue coupling between the two coils by wayof the leakage elds emanating from the screening cans 3. across the apertures for thel gear wheels II.

What I claim is:

1. An inductance coil system. suitablefor use in radio receivers and the like comprisinga plurality of tubular enclosures of non-magneticmaterial, each of. said enclosureshaving alongitu.- dinal axis, a U-shapedy frame, a resilient plate secured to said U-shaped frame and supporting said enclosures in parallel axial alignment, each of said enclosures housing a coil Wound on a hollow tubular form of insulating material, a core having a given axis parallel to the axis of the enclosure slideable' within the form, a transverse member. slideable withintlfie. enclosure supporting the core, a rod of ferrite material having a magnetic permeability of at least adjustably secured.. torsaid transverse member and movable therewith, saidY rod of ferrite material being mounted parallel to the axis of the core and at the endof saidficore remote from the end which enters thetubular form, and means to conjointly move the-respective transverse members in each enclosurecomprisingl a driving member journalledvinthef ends of the limbs of the U-shaped member, a gearing Wheel mounted on said driving'member for each transverse member, and a toothed rack secured to each transverse member and engaging one of saidgear wheelsfor transmitting movement of said gear wheel to' saidl transverse member thereby`- movi-ngV the latter.

2; An. inductanceassembly as claimed in claimporting said core at an end thereof remote fromr the end which enters said tubular form, and a rod of ferrite material having a-*magnetic permeability of at least 10'0 slideably-securedto said trans-- verse member andfmoveable therewith, said rod of` ferritematerial being mountedapproximately parallel to the axis of saidcore adjacent the inner wall ofv said tubular member;

4; An inductance coil suitableforusein radio receivers andthe-likey comprising a tubular enclosure'ofnon-magnetic material, a coil wound on a hollow tubularl form'of insulating'material within said enclosure, av core having a given axis slideable within said form, a tubular member of'v non-magnetic material surrounding said form andmoveable withinl said4 enclosure,` a transverseA member of non-magnetic material secured-to said tubular member forl` -movementtherewith and supporting said core at an endthereofremotek from the-end vwhich enters sai-d tubular-form, and a rod-of ferrite material having a magnetic permeability of at least lislideablyttingin an opening of said l'transverse ymember and vmoveable i therewith, said rod of ferrite material being mounted approximately parallel to the axisof said core adjacent the inner'wall ofsaid'tubular member.

5: An'inductance coil` suitable foruseinv radio receiversV andl the like comprising aV tubular enclosureof'non-magnetic material, a coil Wound on a hollow Y' tubular formY ofv insulating 'material within-said enclosure, a corehavinga given axis moveable within saidform, atubular. member of non-magnetic material' surrounding said form.

and being moveably arranged.` within said' enclosure, of nonfmagnetic. material securedY to:A a. transverse wall. por-tion ofsaid slideable tubular.- member for movement therewith and supporting.- said-core at the. end remote fromithe endwhich.

enters the tubular form, a rod of ferrite material having a magnetic permeability of at least 100 extending through an aperture in said transverse Wall portion adjacent the inner wall of said tubular member, and a resilient member urging said rod against the inner Wall of said tubular member.

6. An inductance coil suitable for use in radio receivers and the like comprising a tubular enclosure of non-magnetic material, a coil Wound on a hollow tubular form of insulating material within said enclosure, a core having a given axis moveable within said form, a tubular member of non-magnetic material surrounding said form and slideable within said enclosure, a transverse member of non-magnetic material secured to said tubular member for movement therewith and supporting said core at an end thereof remote from the end of said core which enters said tubular form, a rod of ferrite material having a magnetic permeability of at least 100 moveably secured to said transverse member and moveable therewith, said rod of ferrite material being mounted approximately parallel to the axis of said core adjacent to the inner wall of said tubular member, and a rod of ferrite material on the side of said core remote from said movable rod and extending approximately parallel to said core for magnetically shielding said coil.

7. An inductance coil suitable for use in radio receivers and the like comprising a tubular enclosure of non-magnetic material, a coil wound on a hollow tubular form of insulating material within said enclosure, a core having a given axis slideable within said form, a tubular member of non-magnetic surrounding said form and being slideably arranged within said enclosure, a transverse wall portion of said slideable tubular member supporting said core for movement therewith at the end of said core remote from the end of the core which enters the tubular form, a rod of ferrite material having a magnetic permeability of at least slideably secured to and extending through an aperture in said transverse wall portion adjacent the inner wall of said tubular member and moveable therewith, and a plurality of spaced rods of ferrite material on the side of said core remote from said movable rod and extending approximately parallel to said core for magnetically shielding said coil.

HENRI MARINUS VISCH.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,137,573 Kamenarovic Nov. 22, 1938 2,448,190 Olesky Aug. 31, 1948 2,458,282 Maki Jan. 4, 1949 FOREIGN PATENTS Number Country Date 347,599 Great Britain Apr. 27, 1931 441,982 Great Britain Jan. 30, 1936 

